Thrust augmenting and sound suppressing apparatus

ABSTRACT

An aircraft jet engine is provided with an ejector nozzle which suppresses jet noise and augments thrust during takeoff and climb. The nozzle is formed as an ejector barrel supported aft of the exhaust nozzle and defines, with the nozzle, inlet passage means for free stream air to enter and mix with engine gases in the mixing zone defined by the barrel. The inner wall of the barrel is formed primarily of acoustical and structural honeycomb paneling perforated on the mixing zone side which suppresses noise and makes the inner wall virtually self supporting. A plenum chamber in the barrel supplies energized gas to an auxiliary jet nozzle in the form of a peripheral slot through the inner wall and receives the gas from the engine through conduits connected to a secondary exhaust nozzle. The latter includes a lobed section in which the side walls of the lobes are formed of acoustical and structural honeycomb to further suppress noise and make the lobe side walls self supporting.

United States Patent [191 Tontini June 5,1973

Primary ExaminerRobe'rt S Ward, Jr.

[54] THRUST AUGMENTING AND SOUND SUPPRESSING APPARATUS AttorneyGe orgeE. Pearson [75] lnventor: Remo Tontini, San Diego, Calif.

[73] Assignee: Rohr Corporation, Chula Vista, [57] ABSTRACT Cahf' Anaircraft jet engine is provided with an ejector noz- [22] Filed: Oct.14, 1971 zle which suppresses jet noise and augments thrust duringtakeoff and climb. The nozzle is formed as an [21} Appl' 189309 ejectorbarrel supported aft of the exhaust nozzle and defines, with the nozzle,inlet passage means for free [52] US. Cl. ..l81/33 HC, 181/33 HD,239/1273, stream air to enter and mix with engine gases in the239/265.13, 239/265 17 mixing zone defined by the barrel. The inner wallof [51] Int. Cl ..B64d 33/06, FOln 1/14, FOln 1/16 the barrel is formedprimarily of acoustical and struc- [58] Field of Search ..l81/33 H, 33HA, r l h neycomb paneling perf rated on the mixing 181/33 HB, 33 BC, 33G, 33 HD, 43, 33 HE, zone side which suppresses noise and makes theinner 51;239/265 11, 265.13, 265,17, 1273 wall virtually selfsupporting. A plenum chamber in the barrel supplies energized gas to anauxiliary jet [56] Referen Cit d nozzle in the form of a peripheral slotthrough the v inner wall and receives the gas from the engine UNITEDSTATES PATENTS through conduits connected to a secondary exhaust 3 477231 11/1969 Paulson ..18l/33 l-lA The latter includes a lobed Sectiowhich 3:516:511 6/1970 Urquhart "181 /33 HC the side walls of the lobesare formed of acoustical 3,533,486 10/1970 Paulson ....1s1/33 HD andStructural honeycomb further pp noise 3,579,993 /1971 Tanner et al...239/127.3 and make the lobe side walls self supporting. 3,618,70011/1971 Bond et al. ..181/33G I FOREIGN PATENTS OR APPLICATIONS 12Claims, 4 Drawing Figures 935,119 8/1963 Great Britain ..l8l/33 HA 54 z5% 62 2s 5o Q50 56 60 x 12 0 t, 8s 1 5 7 2 |I l I -1 ri r381. 4O 7 72 44"l 1 V l l. I n/ I 8 36 2O 88 Patented June 5, 1973 i 3,731,005

2 Sheets-Sheet 2 INVENTOR. REMO TONTINI 1 M ATTORNEY TIIRUST AUGMENTINGAND SOUND SUPPRESSING APPARATUS BACKGROUND OF THE INVENTION Thisinvention lies in the field of gas turbine or jet engines which producereaction thrust by the high velocity rearward discharge of exhaust gasesfrom the engines. In order to obtain the maximum thrust from a simpleengine a great deal of study and calculation goes into the design of theexhaust nozzle, and for best reoutside of the turbine and joining theturbine exhaust.

The mixing of the two gases adds mass to the thrust producing stream andreduces the velocity and temperature thereof, which also reduces thenoise level.

Another system which is used extensively includes the provision of anejector barrel which is larger than the exhaust nozzle outlet and islocated aft of the nozzle. Free stream air enters the flow path betweenthe exhaust nozzle and the barrel and mixes with the exhaust gas, andalso with the fan air if the engine is of the fan type. All of the gasesmix within the barrel with the same general effects mentioned above.

When an ejector barrel is used with a lobed or daisy nozzle, furthernoise suppression is achieved because free stream air meets turbine gasalong a much greater marginal path than with a simple nozzle to greatlyincrease the mixing effect. The pressures and vibration forces withinlobed nozzles and ejector barrels are very great and normally they areprovided with many heavy and complicated bracing members to help them towithstand these forces and prevent failure. Also, the jet stream noiselevel is still undesirably high even with the suppression effects of thelobed nozzle and the ejector barrel.

SUMMARY OF THE INVENTION a shorter and lighter ejector barrel. In anyform itincreases noise suppression and provides great strength andrigidity of the components while substantially reducing bracing memberswhich add weight and often impede free flow of the gases.

Generally stated, and in presently preferred forms, the total apparatusincludes a jet engine having a rearwardly discharging exhaust nozzlewhich may be divided into a primary nozzle and a secondary nozzleattached thereto and having a conventional lobed form in its aftportion. An ejector barrel is located aft of the nozzle and preferablywith its entrance end in the vicinity of the exit margin of the exhaustnozzle. Preferably the forward end of the barrel is attached to theouter ends of the lobes at or near the nozzle exit margin, and thevalleys between the lobes provide paths for inflow of free stream air tomix with the engine gas in the mixingzone defined by the barrel.

need for bracing members is almost completely eliminated. In addition,the inner surface of the inner wall is provided with a multiplicity ofapertures therethrough communicating with the honeycomb core cells toprovide resonating cavities which act to suppress the sound energy ofthe gases flowing through the barrel.

The same forces are present within each of the lobes of the exhaustnozzle and tend to force the generally planar walls of the lobe apart.Tie rods extending across the lobe interiors'between the walls resistthese forces but at the same time they interfere with the free flow ofthe gases. In order to overcome this difficulty in the presentinvention, the side walls of each lobe are formed of metallic acousticaland structural honeycomb which provides so much strength and rigiditythat no tie rods are needed. In addition the inner faces of the wallsare perforated as in the case of the ejector barrel to increase thenoise suppression. The forward or first section of the secondary nozzleis generally cylindrical and is also formed of metallic acoustical andstructural honeycomb to still further increase the noise suppression.This first section so constructed is so strong and rigid that it servesas a cantilever member to support the second section and the ejectorbarrel and to attach them to the primary exhaust nozzle.

The thrust and efficiency of the assembly may be further increased bydividing the inner wall of the ejector barrel into forward and aftsections separated by a peripheral slot which serves as an auxiliary jetnozzle to discharge energized gas in a ring around the periphery of themixed gases flowing through the ejector barrel and add energy thereto. Aplenum chamber in the ejector barrel receives energized gas from theengine through conduits connected to the exhaust nozzle and the plenumchamber, and communicates with the jet nozzle through which the gas isdischarged. Portions of the ejector barrel aft of the jet nozzle may bemade separate and pivoted on transverse axes to serve as blocker doorsswinging rearwardly and inwardly toward each other to block the jetstream and produce reverse thrust.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 4 is a sectional view taken online 44 of FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS An installation incorporating theinvention is shown schematically in FIGS. 1 and 2, in which a jetengine, not shown, is provided with a rearwardly discharging primaryexhaust nozzle 10 having a first central duct 12 discharging turbine gasand a second peripheral duct 14 surrounding the first duct anddischarging fan air, with both ducts terminating at exit plane 16. Anacelle l8 surrounds the engine and primary exhaust nozzle.

A secondary exhaust nozzle includes a first generally cylindricalsection 22 and a second section 24 in the form of a lobed or daisynozzle having an exit plant 26, the two sections being permanentlysecured together. As shown in FIG. 3, the first section is provided withan annular flange 28 which is secured to the standard engine flange 30by a series of bolts 32. Web 34, secured to flange 28, carries a fairing36 to complete the contour of the nacelle. The lobes 38 are peripherallyspaced and extend radially and axially to divide the gas flow intoseparate streams, and between them they define valleys which provideflow paths 40 for free stream air to enter and mix with the enginegases.

An ejector barrel 42 is connected at its entrance end 44 to the radiallyouter ends of the lobes and is located aft of the nozzle with itsentrance end 44 in the vicinity of exit plane 26. The interior of thebarrel defines a mixing zone 46 where the free stream air meets with theengine gases to mix with them and add mass to the flow, increasing thethrust and reducing the noise level in known manner. The inner wall 48of the barrel is formed primarily of metallic acoustical and structuralhoneycomb paneling which is so rigid and strong that the wall is able toresist the gas pressure and vibration forces with little or no supportin the form of bracing members. The inner surface of wall 48 is providedthroughout its area with a multiplicity of apertures 50 therethroughcommunicating with the honeycomb core cells to provide resonatingcavities which suppress the noise of the propulsion flow. v

The lobed nozzle section 24 is subject to the same high destructiveforces as the inner wall of the ejector barrel. The form andconstruction of the lobes are shown in FIG. 4. The gas pressure withineach lobe 38 tends to force its walls 52 apart, and this loadingcombined with the vibration forces tends to cause failure. Instead ofusing a plurality of tie bolts which interfere with gas flow, each sidewall 52 is formed of the same type of paneling as wall 48. Thus thepanels are rigid enough to retain their shape and strong enough toresist the forces imposed on them. The inner surfaces of walls 52 areperforated throughout their area and thus increase the total amount ofsound suppression.

The first section 22 is also subjected to the destructive forces of gaspressure and vibration and is likewise formed of metallic acoustical andstructural honeycomb paneling. This paneling further suppresses jetstream noise and is so strong and rigid that section 22 serves as acantilever member to support section 24 and ejector barrel 42. Theentire assembly is made unitary and may be readily applied as a retrofitto any existing engine by removing the section aft of the primary nozzleand bolting the new assembly to the standard engine flange.

The effectiveness of the apparatus may be further improved by theaddition of means for producing a ring or shield of energized gas aroundthe gaseous mixture in the ejector barrel to add energy to the totalfiow and flatten the velocity profile which increases thrust and reducesnoise. As seen in FIG. 2, the inner wall 48 of the ejector barrel isdivided into a forward section 54 having a trailing edge 56 and an aftsection 58 having a leading edge 60 spaced from trailing edge 56 todefine a peripheral slot 62 through the wall serving as an auxiliary jetnozzle. A partition 64 extends around the periphery of the interior ofthe ejector barrel and from a forward point 66 of the outer wall 68 tothe leading edge 60 of the inner wall. It is smooth and imperforate andcooperates with the smooth and imperforate outer surface of the innerwall 48 to define a plenum chamber 70 which is devoid of anyobstructions which would impede the flow of gas through the plenumchamber.

Conduits 72 are connected at their aft ends to the plenum chamber and attheir forward ends to nozzle section 22 at its periphery. They are inlongitudinal alignment with fan air duct 14 and thus receive primarilyfan air which passes through the conduits to the plenum chamber andthence out through jet nozzle 62. It will be noted that rearwardlyconverging partition 64 cooperates with the inner wall section 54 toimpart a somewhat rearwardly converging path to the exiting gas stream.The leading edge 60 of section 58 is peripherally larger than thetrailing edge 56 of section 54 to cause the jet nozzle exit to faceprimarily rearward and cooperate with the converging path of the gasstream. The flow from the jet nozzle produces a virtual nozzle profilefor the aft section of the ejector barrel which depends on the energy ofthe flow. This virtual nozzle profile is selected for optimumperformance and is achieved by tailoring the jet nozzle shape and gasflow amount for each particular installation.

As previously stated, conduits 72 overlie the outer ends of the lobes 38to leave valleys 40 clear for the inflow of free stream air. As seen inFIG. 4, the inner wall 74 of each conduit also serves as the outer endwall of each lobe, and they share this common wall throughout the majorpart of their lengths. All of these components are welded into unity sothat the conduits and lobes serve to mutually reinforce each other.

Because of the strong and rigid construction of the ejector barrel andthe fact that the jet nozzle is well forward of the exit end 76 of thebarrel, it is very simple to install thrust reversing means. As can beseen in FIGS. 1 and 2, portions of the ejector barrel may be cut away toform openings 78 in which blocker doors 80 are located. The doors arepivoted on transverse axes 82 and operated by a conventional servo motor84 and linkage 86 to swing from stowed position shown in solid linesrearward and inward toward each other until their trailing edges 88contact each other at the axis of the ejector barrel to block rearwardflow of the jet stream and redirect it laterally and forwardly toproduce reverse thrust. While the doors may be of any construction,their inner walls preferably are made of the same honeycomb paneling asthe wall 58 because the forces on them during thrust reversal are veryhigh. Their outer walls may be single thickness skin with simplestringers for bracing.

Having thus described the invention, what is now claimed as new anduseful and is desired to be protected by US. Letters Patent is:

1. Apparatus for augmenting the thrust and suppressing the exhaust noiseof a jet engine having a rearwardly discharging exhaust nozzle,comprising: an ejector barrel having an entrance end and an exit end;the ejector barrel being located in operative position aft of theexhaust nozzle with its entrance end adjacent to the nozzle exit andspaced at least in part from the nozzle to define inlet path means forthe flow of free stream air; the barrel defining a mixing zone for thefree stream air and the gas stream issuing from the nozzle; the innerwall of the barrel being divided into a forward section and an aftsection; the leading edge of the aft section being spaced from thetrailing edge of the forward section to define between them a rearwardlydischarging auxiliary jet nozzle in the form of a peripheral slotthrough the inner wall; and means to supply gas under pressure to thejet nozzle to peripherally surround the gaseous stream and add energythereto; the inner walls of the forward and aft sections being formedprimarily of metallic acoustical and structural honeycomb panelingserving to make the walls self supporting and sound suppressing; theinner surfaces of the walls exposed to the mixing zone being providedwith a multiplicity of apertures communicating with the honeycomb corecells to provide resonating cavities to suppress the sound energy of thegaseous stream.

2. Apparatus as claimed in claim 1; and a smooth imperforate partitionextending around the interior of the barrel and from its outer wall tothe leading edge of the inner wall of the aft section; the outer surfaceof the forward inner wall being smooth and imperforate; the partitionand the inner wall defining between them an annular plenum chamber forthe jet nozzle which is devoid of flow obstructions; and conduit meansextending between the engine exhaust nozzle and the plenum chamber toconduct energized gas from the engine to the plenum chamber.

3. Apparatus as claimed in claim 2; the partition converging rearwardlyfrom the forward end of the plenum chamber to cooperate with the forwardinner wall in directing the energized gas convergently rearward throughthe jet nozzle.

4. Apparatus as claimed in claim 3; the leading edge of the aft innerwall being peripherally larger than the trailing edge of the forwardinner wall to cause the jet nozzle exit to face primarily rearward.

5. Apparatus as claimed in claim 1; portions of the inner and outerwalls of the aft section of the ejector barrel being separate from themain body thereof and being pivotally mounted on transverse axes toswing rearwardly and inwardly toward each other to serve as thrustreversing blocker doors.

6. Apparatus as claimed in claim 5; the inner walls of the blocker doorportions in stowed position defining portions of the honeycomb panelinner wall construction of the aft section of the ejector barrel.

7. Apparatus for augmenting the thrust and suppressing the exhaust noiseof a jet engine having a rearwardly discharging primary exhaust nozzlehaving attachment means in the general plane of the nozzle exit,comprising: a secondary exhaust nozzle having a first generallycylindrical section provided at its leading edge with attachment meansfor connection to the attachment means of the primary exhaust nozzle,and a second section in direct continuation of the first section andhaving the form of a lobed nozzle with a plurality of peripherallyspaced radially and axially extending lobes defining between themvalleys for the inflow of free stream air; an ejector barrel having anentrance end and an exit end; the ejector barrel being located inoperative position aft of the lobed nozzle with its entrance endadjacent to the nozzle exit and being secured to the radially outer endsof the lobes to support it in position; the barrel defining a mixingzone for the free stream air and the gas stream issuing from the nozzle;the inner wall of the barrel being formed primarily of metallicacoustical and structural honeycomb paneling serving to make the wallself supporting and sound suppressing; the inner surface 'of the wallexposed to the mixing zone being provided with a multiplicity ofapertures communicating with the honeycomb core cells to provideresonating cavities to suppress the sound energy of the gaseous stream;the side walls of. each lobe of the secondary exhaust nozzle beingformed of metallic acoustical and structural honeycomb paneling servingto make them self supporting and sound suppressing; the inner surface ofeach side wall exposed to the exhaust gases being provided with amultiplicity of apertures communicating with the honeycomb core cells toprovide resonating cavities.

8. Apparatus as claimed in claim 7; the first section of the secondaryexhaust nozzle also being formed of metallic acoustical and structuralhoneycomb paneling with its inner surface provided with a multiplicityof apertures communicating with the honeycomb core cells to provideresonating cavities; the first section serving as a cantilever member tosupport the second section and the ejector barrel.

9. Apparatus as claimed in claim 7; the inner wall of the ejector barrelbeing divided in a lateral plane intermediate the ends of the barrel toprovide a peripheral slot serving as an auxiliary jet nozzle; theforward portion of the barrel being hollow to serve as a plenum chambercommunicating with the jet nozzle; and a plurality of longitudinallyextending conduits connected at their aft ends to the plenum chamber andat their forward ends to the first section of the secondary nozzle atits periphery to conduct energized gas from the engine to the plenumchamber; eachof the conduits overlying the outer end of one of the lobesto leave the valleys between the lobes clear for the inflow of freestream air.

10. Apparatus as claimed in claim 9; each conduit being unitedthroughout the major portion of its length with the outer end of itsassociated lobe for mutual reinforcement.

11. Apparatus as claimed in claim 9; the primary exhaust nozzle beingdivided into a first central duct discharging turbine gas and a secondperipheral duct surrounding the first duct and discharging fan air; theforward ends of the conduit at the periphery of the first section of thesecondary nozzle being in longitudinal alignment with the second duct toreceive primarily fan air for transfer to the plenum chamber.

12. Apparatus for augmenting the thrust and suppressing the exhaustnoise of a jet engine having a rearwardly discharging exhaust nozzle,comprising: an ejector barrel having an entrance end and an exit end;the ejector barrel being located in operative position aft of theexhaust nozzle with its entrance end adjacent to the nozzle exit andspaced at least in part from the nozzle to define inlet path means forthe flow of free stream air; the barrel defining a mixing zone for thefree stream air and the gas stream issuing from the nozzle; the innerwall of the barrel being formed primarily of metallic acoustical andstructural honeycomb paneling serving to make the wall self supportingand sound suppressing; the inner surface of the wall exposed to themixing zone being provided with a multiplicity of aperturescommunicating with the honeycomb core cells to provide resonatingcavities to suppress the sound energy of the gaseous stream.

1. Apparatus for augmenting the thrust and suppressing the exhaust noiseof a jet engine having a rearwardly discharging exhaust nozzle,comprising: an ejector barrel having an entrance end and an exit end;the ejector barrel being located in operative position aft of theexhaust nozzle with its entrance end adjacent to the nozzle exit andspaced at least in part from the nozzle to define inlet path means forthe flow of free stream air; the barrel defining a mixing zone for thefree stream air and the gas stream issuing from the nozzle; the innerwall of the barrel being divided into a forward section and an aftsection; the leading edge of the aft section being spaced from thetrailing edge of the forward section to define between them a rearwardlydischarging auxiliary jet nozzle in the form of a peripheral slotthrough the inner wall; and means to supply gas under pressure to thejet nozzle to peripherally surround the gaseous stream and add energythereto; the inner walls of the forward and aft sections being formedprimarily of metallic acoustical and structural honeycomb panelingserving to maKe the walls self supporting and sound suppressing; theinner surfaces of the walls exposed to the mixing zone being providedwith a multiplicity of apertures communicating with the honeycomb corecells to provide resonating cavities to suppress the sound energy of thegaseous stream.
 2. Apparatus as claimed in claim 1; and a smoothimperforate partition extending around the interior of the barrel andfrom its outer wall to the leading edge of the inner wall of the aftsection; the outer surface of the forward inner wall being smooth andimperforate; the partition and the inner wall defining between them anannular plenum chamber for the jet nozzle which is devoid of flowobstructions; and conduit means extending between the engine exhaustnozzle and the plenum chamber to conduct energized gas from the engineto the plenum chamber.
 3. Apparatus as claimed in claim 2; the partitionconverging rearwardly from the forward end of the plenum chamber tocooperate with the forward inner wall in directing the energized gasconvergently rearward through the jet nozzle.
 4. Apparatus as claimed inclaim 3; the leading edge of the aft inner wall being peripherallylarger than the trailing edge of the forward inner wall to cause the jetnozzle exit to face primarily rearward.
 5. Apparatus as claimed in claim1; portions of the inner and outer walls of the aft section of theejector barrel being separate from the main body thereof and beingpivotally mounted on transverse axes to swing rearwardly and inwardlytoward each other to serve as thrust reversing blocker doors. 6.Apparatus as claimed in claim 5; the inner walls of the blocker doorportions in stowed position defining portions of the honeycomb panelinner wall construction of the aft section of the ejector barrel. 7.Apparatus for augmenting the thrust and suppressing the exhaust noise ofa jet engine having a rearwardly discharging primary exhaust nozzlehaving attachment means in the general plane of the nozzle exit,comprising: a secondary exhaust nozzle having a first generallycylindrical section provided at its leading edge with attachment meansfor connection to the attachment means of the primary exhaust nozzle,and a second section in direct continuation of the first section andhaving the form of a lobed nozzle with a plurality of peripherallyspaced radially and axially extending lobes defining between themvalleys for the inflow of free stream air; an ejector barrel having anentrance end and an exit end; the ejector barrel being located inoperative position aft of the lobed nozzle with its entrance endadjacent to the nozzle exit and being secured to the radially outer endsof the lobes to support it in position; the barrel defining a mixingzone for the free stream air and the gas stream issuing from the nozzle;the inner wall of the barrel being formed primarily of metallicacoustical and structural honeycomb paneling serving to make the wallself supporting and sound suppressing; the inner surface of the wallexposed to the mixing zone being provided with a multiplicity ofapertures communicating with the honeycomb core cells to provideresonating cavities to suppress the sound energy of the gaseous stream;the side walls of each lobe of the secondary exhaust nozzle being formedof metallic acoustical and structural honeycomb paneling serving to makethem self supporting and sound suppressing; the inner surface of eachside wall exposed to the exhaust gases being provided with amultiplicity of apertures communicating with the honeycomb core cells toprovide resonating cavities.
 8. Apparatus as claimed in claim 7; thefirst section of the secondary exhaust nozzle also being formed ofmetallic acoustical and structural honeycomb paneling with its innersurface provided with a multiplicity of apertures communicating with thehoneycomb core cells to provide resonating cavities; the first sectionserving as a cantilever member to support the second section and theejector barrel.
 9. Apparatus As claimed in claim 7; the inner wall ofthe ejector barrel being divided in a lateral plane intermediate theends of the barrel to provide a peripheral slot serving as an auxiliaryjet nozzle; the forward portion of the barrel being hollow to serve as aplenum chamber communicating with the jet nozzle; and a plurality oflongitudinally extending conduits connected at their aft ends to theplenum chamber and at their forward ends to the first section of thesecondary nozzle at its periphery to conduct energized gas from theengine to the plenum chamber; each of the conduits overlying the outerend of one of the lobes to leave the valleys between the lobes clear forthe inflow of free stream air.
 10. Apparatus as claimed in claim 9; eachconduit being united throughout the major portion of its length with theouter end of its associated lobe for mutual reinforcement.
 11. Apparatusas claimed in claim 9; the primary exhaust nozzle being divided into afirst central duct discharging turbine gas and a second peripheral ductsurrounding the first duct and discharging fan air; the forward ends ofthe conduit at the periphery of the first section of the secondarynozzle being in longitudinal alignment with the second duct to receiveprimarily fan air for transfer to the plenum chamber.
 12. Apparatus foraugmenting the thrust and suppressing the exhaust noise of a jet enginehaving a rearwardly discharging exhaust nozzle, comprising: an ejectorbarrel having an entrance end and an exit end; the ejector barrel beinglocated in operative position aft of the exhaust nozzle with itsentrance end adjacent to the nozzle exit and spaced at least in partfrom the nozzle to define inlet path means for the flow of free streamair; the barrel defining a mixing zone for the free stream air and thegas stream issuing from the nozzle; the inner wall of the barrel beingformed primarily of metallic acoustical and structural honeycombpaneling serving to make the wall self supporting and sound suppressing;the inner surface of the wall exposed to the mixing zone being providedwith a multiplicity of apertures communicating with the honeycomb corecells to provide resonating cavities to suppress the sound energy of thegaseous stream.